Assessment of impacts of land use changes on water resources of river Mpanga catchment

Abstract

Mpanga Catchment has in recent decades been exposed to changes in land use/cover (LULC). This could have been due to intensive agricultural activities to sustain the needs of the increasing population. Transition in land use/cover tends to impact on the hydrology of a given catchment. This study assessed the impacts of land use changes on water resources of Mpanga catchment. The study was three-fold. Firstly, land use changes were identified and analysed. In the second step, the question of whether land use changes impacted on water resources was answered through hydrological modelling using Soil and Water Assessment Tool (SWAT). SWAT was automatically calibrated and validated using daily data from 2003 to 2013. Thirdly, the model was applied to conduct scenario analysis. Major land use/covers included cropland, forest, pasture, wetland, water body and settlement. Cultivated area increased by 31.79% while grassland and forests decreased by 31.79% and 11.38%, respectively. Hydrological model performance evaluation yielded Nash-Sutcliffe model efficiency (NSE) 0.86 and 0.77 during calibration and validation periods, respectively. Changes in the land uses between 2000 and 2014 increased stream flow ratios from 0.49 to 0.54, surface runoff from 0.26 to 0.33 and evapotranspiration ratios reduced from 0.49 to 0.44. Scenario analysis showed that the catchment was more influenced by the land use changes with respect to dry than wet conditions. Thus, control measures like agroforestry, deep tillage and banding should be adopted to minimize run off and facilitate infiltration and ground water recharge. Key words: Catchment, land use/cover, water resources, scenarios, hydrological modelling